1. Field of the Invention
The present invention relates to a wireless communication method using orthogonal frequency division multiplexing (OFDM), an OFDM receiving method and an apparatus thereof.
2. Description of the Related Art
In a multipath channel, in an environment where signals arrive with different propagation delay time, wave distortion caused by intersymbol interference can be a major factor of deteriorating communication quality. An orthogonal frequency division multiplexing (OFDM) scheme is known as a scheme to reduce wave distortion which occurs when receiving signals with different propagation delay time.
When performing frequency conversion to convert signals of a baseband to signals of a high frequency band, a wireless transmitter uses a quadrature modulator. In the case where this quadrature modulator is comprised of an analogue circuit, the incompleteness of the analogue circuit causes an amplitude error or a phase error between an inphase component and a quadrature component, which is referred to as IQ imbalance. In the case where the IQ imbalance occurs in the quadrature modulator, two subcarrier signals (subcarrier pair) among the OFDM signal subcarriers, which are symmetric with respect to a center frequency, interfere with each other. Such mutual interference significantly deteriorates receiving quality.
To eliminate mutual interference between the subcarrier pairs, JP-A 2001-119364 (KOKAI) suggests a scheme to estimate and compensate mutual interference quantity caused by IQ imbalance for each subcarrier pair. In this scheme, a channel estimation preamble signal consisting of a particular structure is transmitted, and the receiving side uses the preamble signal to estimate the mutual interference quantity between the subcarriers caused by the IQ imbalance.
As mentioned above, when estimating the mutual interference quantity between each subcarrier pair caused by IQ imbalance, the technique described in JP-A 2001-119364 (KOKAI) uses a different particularly structured channel estimation preamble signal for each subcarrier pair. Therefore, there is a problem that the overhead of the channel estimation preamble signal increases.